Enzymes regulating the levels of cyclic nucleotides in cells govern some of the most important biological control systems. Control of cyclic nucleotide levels relates to the well-known intracellular expression of hormonal action, increasingly to the dynamics of cell division regulation, and more recently, possibly to the psychodynamics of human emotion and mental illness. Very little is known of the specific kinetic characteristics of enzymes catalyzing the conversion of the nucleoside triphosphates to the cyclic nucleotides, and enzymes catalyzing their subsequent hydrolysis to inactive species. Detailed kinetic study is critical to an understanding of specific molecular features which will allow differential drug design to selectively manipulate levels of cyclic AMP and cyclic GMP in cells. The goal of this laboratory for the past two years has been the selective design of agents to inhibit adenylate cyclase in intact cells, allowing possible treatment agents for the cyclic-AMP-mediated disease cholera and experimental probes for hypotheses of cell division regulation. Success has been achieved in finding a series of compounds, R-O-PO3-R, the phosphate diesters, which pass through some cell membranes to inhibit adenylate cyclase in situ. The proposed work deals with refinement of the nature of the R groups to determine compounds that pass through membranes with the greatest efficiency, show the least toxicity in degradation products, and show specificity for particular target tissues. A second, related area of our work deals with the behavior of cyclic nucleotide phosphodiesterase in a possible role in cell division regulation. Several phosphodiesterases exist in cells, probably having different roles, and presenting a complex kinetic picture. We are attempting to use kinetic study to select out the phosphodiesterase species most likely to be involved in cell division regulation. We will then attempt selective manipulation of this enzyme.